Gas turbine engines are used extensively in high performance aircraft and they employ compressors, combustors and turbines that generate massive air flows that circulate throughout the engine's systems. By controlling the air flow greater efficiencies and economical performance can be achieved which is desired in the competitive airline industry.
Gas turbine engine combustors are subjected to and must meet stringent emission standards. This means that the temperatures within the combustors may increase as cooling air is diverted to the inside of the combustor to control emissions. A combustor can have an inner and outer liner, and tiles can be used to line the inner wall of combustor to aid in thermal control and dissipation. Tiles can have a maximum operating temperature of about 1150° C. and are desirable to use in such extreme operating conditions. Controlling air flow across the tiles and in between the tiles that line a combustor is a challenge as traditional sealing systems have deficiencies that have yet to be resolved.
Combustor tiles may be constructed of ceramic matrix composite material. Mechanical seals, such as a leaf seal, however are typically metallic in construction and operate primarily by pressure being exerted on a moving member of the seal. As pressure is exerted on the seal, it tends to cause the moving member to deflect and move towards a closed position which in turn may close off a fluid flow path that may be located between combustor tiles or in proximity of the combustor. Such arrangement allows the seal to manipulate between an open fluid flow position and a closed fluid flow position. A spring may be employed to aid in influencing the seal to an open or closed position, depending on the arrangement of the seal. In environments where operating temperatures exceed the operating capacity of springs, it may not be permissible to use conventional seals.
A leaf seal tends to relax at elevated temperatures. And in environments where there is inadequate pressure to force a leaf seal to move, it may not perform adequately. For example, if the operating pressure is too low, the seal member may not move, and thus, it may not close off the fluid flow path. Such characteristic would not be helpful in arrangements where it is desired to close off fluid flow paths that operate between combustor liners and surrounding combustor tiles.
Thus, a problem exists with sealing combustion liners and controlling flow paths in low pressure and high temperature settings. Mechanical seals have been used but lack the flexibility necessary for this environment. Accordingly, an exemplary seal system will create a seal even when there is insufficient pressure to force a seal into position. Employing a seal system that operates irrespective of pressures within the system would be helpful to the aircraft industry and to other industries where controlling fluid low in low pressure settings is desirable.